1. Field of the Invention
The present invention relates to a gas generator for an air bag which can inflate an air bag securely and can securely obtain such an operation performance as designed, and an air bag system using the same.
2. Description of the Related Art
With a development of a gas generator used in an inflating-type safety system of motor vehicles, a hybrid type gas generator using both a pressurized gas and a gas generating agent is attracting attention. This hybrid type gas generator is one which accommodates a pressurized gas hermetically, releases and discharges the sealed pressurized gas to inflate an air bag in cooperation with a combustion gas generated by a solid gas generating agent.
Since such a hybrid type gas generator must be activated securely when required, a mechanism for securely releasing a sealed pressurized gas charged in the interior of a housing. In many cases, a rupturable plate is used as sealing means for a pressurized gas, and the sealed state is released by rupturing this rupturable plate. Then, for rupturing the rupturable plate, a pressure in a pressurized gas accommodating space, which is raised by a flame (or by heat, hereinafter, which is used in the same manner) or a gas generated due to combustion of a solid gas generating agent, breaking a sealing member with a projectile or a moving body, or an impact wave, a flame, a gas generated at a time of activation of an igniter, or the like is used. In rupturing the rupturable plate securely to secure activation of the gas generator, it is especially desirable to rupture the sealing member by using the projectile, the moving body or the like among these means.
In recent years, regarding the hybrid type gas generator, one, which can adjust the degree of inflation of an air bag in response to an impact to restrain a passenger at the activation, has been provided. Specifically, such a gas generator is generally constituted such that two igniters which can be activated individually and independently are included, and rupturable plates corresponding to respective igniters are provided, discharge of a gas starts when a main rupturable plate is ruptured by activation of a main igniter and an amount of a discharged gas is increased when an auxiliary igniter is activated. In order to guarantee a reliable rupture of the main rupturable plate, as described above, a hybrid type gas generator using a projectile or a moving body has also been provided.
As a gas generator in which the degree of inflation of an air bag can be adjusted, a hybrid type gas generator in which a pressurized gas, and solid gas generating agents accommodated in a plurality of combustion chambers has also been known.
For example, German patent publication DE19933551A1 discloses a hybrid type inflating apparatus provided with two charges, which can be ignited at predetermined time accurately without any mutual influence, has been shown. The hybrid type inflating apparatus is constituted such that an opening of a gas chamber accommodating a compression gas is closed by a rupturable plate, charges are provided on both sides of the gas chamber, and closing means for closing the opening of the gas chamber is removed by pressing a piston (a plug body) due to combustion of the charges.
However, the piston (the plug body) shown in this document is in contact with the rupturable plate before activation, and a remarkable energy (pressure) is required for pushing a moving body. For this reason, the moving body is hard to move, and it becomes difficult to remove the rupturable plate reliably. In some cases, there is a possibility that an internal pressure in a charge chamber rises abnormally, and breaks a housing. Particularly, it is considerably important to remove the rupturable plate securely and improve an operation security of a gas generator for an air bag because of the relationship with the usage thereof.
Further, when an inflation degree of an air bag is adjusted according to an impact, it is important to activate a gas generator as designed, and therefore it is needed that rupturable plates provided to correspond to respective igniters are ruptured due to only activation of the corresponding igniters and they are not ruptured unintentionally.
Furthermore, since complication of the structure of a gas generator causes increases in number of manufacturing steps and manufacturing cost and an increase in volume of the gas generator causes inconvenience in relationship with an arrangement space, it is necessary to avoid complication of the structure of the gas generator and an increase of the volume thereof.
However, a gas generator for an air bag satisfying all the above requirements has not been provided yet.